Reply by Swyftfeet

Open the battery pack case, they usually have an array of small batteries. Figure out the battery size, they are labeled most times. If not, take the voltage and divide by number of batteries.

Order a bunch of rechargeable replacements for for 1/15th of what you could buy a replacement pack. Some solder and back to work… Done it a couple of times on an old NiiCad for the old man. He gets about 2-4 more years every time.